SSL/TLS Alert Protocol & the Alert Codes

Події від SChannel можна частенько побачити в журналі System Windows сервера. Вони сигналізують про проблеми з SSL/TLS і зазвичай відображають це кодом помилки. Механізм журналювання являється частиною протоколу SSL/TLS.
Для отримання детальних відомостей журналювання SChannel повинно бути ввімкнене. Як це зробити описує відповідна стаття:

Ці події можуть бути дуже корисними при вирішенні проблем, що стосуються SSL. Проте, нажаль, не так багато документації детально описує коди помилок подій SChannel.
Ці коди визначені у  TLS/SSL RFC для усіх існуючих версій протоколу. Наприклад, розглянемо RFC 5246 (TLS 1.2). Цей RFC визначає коди помилок для найновішої версії протоколу.

Перевірте це посилання:

Нижче приведено частину RFC, що визначає коди помилок:

A.3. Alert Messages

enum { warning(1), fatal(2), (255) } AlertLevel;
enum {
unsupported_extension(110), /* new */
} AlertDescription;
struct {
AlertLevel level;
AlertDescription description;
} Alert;

Ця MSDN стаття також описує ці коди:

Таблиця нижче поєдує у собі  матеріали з MSDN із інформацією з RFC:

Alert Code Alert
0 close_notify Notifies the recipient that the sender will not send any more messages on this connection.
10 unexpected_message Received an inappropriate message This alert should never be observed in communication between proper implementations. This message is always fatal.
20 bad_record_mac Received a record with an incorrect MAC. This message is always fatal.
21 decryption_failed Decryption of a TLSCiphertext record is decrypted in an invalid way: either it was not an even multiple of the block length or its padding values, when checked, were not correct. This message is always fatal.
22 record_overflow Received a TLSCiphertext record which had a length more than 2^14+2048 bytes, or a record decrypted to a TLSCompressed record with more than 2^14+1024 bytes. This message is always fatal.
30 decompression_failure Received improper input, such as data that would expand to excessive length, from the decompression function. This message is always fatal.
40 handshake_failure Indicates that the sender was unable to negotiate an acceptable set of security parameters given the options available. This is a fatal error.
42 bad_certificate There is a problem with the certificate, for example, a certificate is corrupt, or a certificate contains signatures that cannot be verified.
43 unsupported_certificate Received an unsupported certificate type.
44 certificate_revoked Received a certificate that was revoked by its signer.
45 certificate_expired Received a certificate has expired or is not currently valid.
46 certificate_unknown An unspecified issue took place while processing the certificate that made it unacceptable.
47 illegal_parameter Violated security parameters, such as a field in the handshake was out of range or inconsistent with other fields. This is always fatal.
48 unknown_ca Received a valid certificate chain or partial chain, but the certificate was not accepted because the CA certificate could not be located or could not be matched with a known, trusted CA. This message is always fatal.
49 access_denied Received a valid certificate, but when access control was applied, the sender did not proceed with negotiation. This message is always fatal.
50 decode_error A message could not be decoded because some field was out of the specified range or the length of the message was incorrect. This message is always fatal.
51 decrypt_error Failed handshake cryptographic operation, including being unable to correctly verify a signature, decrypt a key exchange, or validate a finished message.
60 export_restriction Detected a negotiation that was not in compliance with export restrictions; for example, attempting to transfer a 1024 bit ephemeral RSA key for the RSA_EXPORT handshake method. This message is always fatal.
70 protocol_version The protocol version the client attempted to negotiate is recognized, but not supported. For example, old protocol versions might be avoided for security reasons. This message is always fatal.
71 insufficient_security Failed negotiation specifically because the server requires ciphers more secure than those supported by the client. Returned instead of handshake_failure. This message is always fatal.
80 internal_error An internal error unrelated to the peer or the correctness of the protocol makes it impossible to continue, such as a memory allocation failure. The error is not related to protocol. This message is always fatal.
90 user_cancelled Cancelled handshake for a reason that is unrelated to a protocol failure. If the user cancels an operation after the handshake is complete, just closing the connection by sending a close_notify is more appropriate. This alert should be followed by a close_notify. This message is generally a warning.
100 no_renegotiation Sent by the client in response to a hello request or sent by the server in response to a client hello after initial handshaking. Either of these would normally lead to renegotiation; when that is not appropriate, the recipient should respond with this alert; at that point, the original requester can decide whether to proceed with the connection. One case where this would be appropriate would be where a server has spawned a process to satisfy a request; the process might receive security parameters (key length, authentication, and so on) at start-up and it might be difficult to communicate changes to these parameters after that point. This message is always a warning.
255 unsupported_extension

Сподіваюся, інформація виявиться корисною при вирішенні помилок TLS/SSL!